The on-board electrical systems of modern motor vehicles are equipped with a large number of electrical loads which serve mainly to implement convenience and comfort functions. Depending on the load, the energy consumption by such on-board systems can be considerable even in standby mode, this possibly leading to complete discharge of the vehicle battery in a worst-case scenario. In this case, energy consumption by the bus system of the on-board system plays a particular role in addition to energy consumption by the individual electrical loads. Modern bus systems are specifically generally designed such that wake up of a load is accompanied by wake up of the entire bus system, this significantly increasing energy consumption.
One of the above convenience or comfort functions is the so-called “keyless entry function”. Known keyless entry systems share the common feature that an, in particular radio-based, authentication dialog is provided between a motor vehicle-side keyless entry control unit and a user-side radio key or the like in order to check the access authorization of the user. After a successful authentication dialog and possibly further operator control events, the motor vehicle is unlocked and/or, depending on the design, a hatch or the like is operated in a motorized manner.
A known arrangement having a keyless entry function (DE 103 33 894 A1) makes provision for the keyless entry control unit to be permanently or cyclically checked in order to determine whether a radio key for the authentication dialog is present. Since this process is associated with correspondingly permanent or cyclical discharging of the vehicle battery, it is proposed to provide an additional energy storage means for the keyless entry function.
In order to reduce energy consumption by the on-board system of a motor vehicle, it has also been proposed to at least temporarily switch over the control unit to an energy-saving standby mode and to wake up said control unit into an operating mode as the situation requires (DE 10 2004 027 541 A1). One requirement for this method which represents the starting point for the present invention is correct switching between the standby mode and the operating mode, specifically in such a way that the respectively desired function is not adversely affected and the system is not susceptible to external influences or misuse.